Water treatment

ABSTRACT

A method treats an aqueous system to inhibit growth of one or more micro-organisms therein and/or to reduce the number of live micro-organisms therein. The method includes adding treatment agents to an aqueous system wherein said treatment agents include (a) a phosphonium compound; and (b) a compound having formula: M(XO 2 ) n  wherein: M is a Group I or Group II metal; X is a halogen; and n is 1 or 2.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 15/152,712 filed May 12, 2016, which is hereby incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to water treatment, particularly thoughnot exclusively, to methods of treating aqueous systems to inhibitgrowth of micro-organisms.

BACKGROUND TO THE INVENTION

The presence and growth of micro-organisms in aqueous systems,especially in industrial water systems, is a concern. Examples ofindustrial water systems where micro-organisms are a concern includecooling water systems, pulping and papermaking systems and oil and gasfield water systems.

The presence of micro-organisms in industrial water systems may resultin the formation of deposits on system surfaces. These deposits or slimecan give rise to various problems. In cooling water systems, slime mayrestrict water flow, reduce heat transfer efficiency, cause corrosionand may be aesthetically unappealing especially if algae are present dueto their visible green pigmentation. Corrosion can also occur inindustrial water systems in the absence of visible slime through theaction of micro-organisms.

In pulp and paper mill systems, slime formed by micro-organisms maycause fouling, plugging, or corrosion of the system. The slime may alsobreak loose and become entrained in the paper produced causingblemishes, holes, tears, and odour in the finished product. The endresult may therefore be unusable product and wasted output.

Slime can also be a problem in oil and gas field water systems and maycause energy losses due to increased fluid frictional resistance,formation plugging and corrosion. The slime may harbour a mixture ofaerobic and anaerobic bacteria that are responsible for the productionof hydrogen sulfide gas. The hydrogen sulfide may cause souring of oiland gas which may reduce the quality of these products and increasetreatment costs.

Pseudomonas aeruginosa bacteria are commonly present in air, water andsoil. These bacteria continually contaminate open cooling water systems,pulping and papermaking systems and oil and gas field water systems andare among the most common slime formers. Slime may be viewed as being amass of cells stuck together by the cementing action of the gelatinoussecretions around each cell. The slime entraps other debris, restrictswater flow and heat transfer and may serve as a site for corrosion.

Chlorella vulgaris algae are also commonly present in air, water andsoil. These algae continually contaminate open cooling water systems andtheir growth turns the water and surfaces in these systems green. Theyalso provide a food source for bacteria, which can stimulate slimeformation, and protozoa which can harbour the pathogenic bacteriumLegionella pneumophila.

A known method of controlling microbial growth in aqueous systems is touse biocides. While biocides are known to inhibit microbial growth, thebiocidal effect is generally of limited duration. The effectiveness ofknown biocides may be rapidly reduced as a result of exposure tonegative influences. Negative influences may include temperature, pH orreaction with ingredients present in the system which neutralizes theirbiocidal effect. Therefore, the use of such biocides may involvecontinuous or frequent addition and their application at multiple sitesor zones in the system to be treated. The cost of the biocide treatmentand the labour costs associated with the application of known biocidesmay therefore be significant.

Known biocides are also highly toxic in the quantities known to berequired for effective control of microbial populations. As a result,the amount of biocides that can be safely discharged into theenvironment may be limited by environmental regulations. Therefore, theneed exists for improved methods for controlling microbial growth inaqueous systems.

As noted above, known biocides have a number of limitations includingthe large quantities of biocides which typically have to be used toachieve the desired biocidal effect and the potential harmful effects onthe environment of biocides and therefore reducing the amount necessaryfor control and thus the quantity released to the environment has manybenefits.

Accordingly, the present invention aims to address at least onedisadvantage associated with the prior art whether discussed herein orotherwise.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method oftreating an aqueous system as set forth in the appended claims. Otherfeatures of the invention will be apparent from the claims, and thedescription which follows.

According to a first aspect of the present invention there is provided amethod of treating an aqueous system to inhibit growth of one or moremicro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to an aqueous system and wherein said treatment agents comprise:

(a) a phosphonium compound; and

(b) a compound having formula:M(XO₂)_(n)

-   -   wherein:    -   M is a Group I or Group II metal;    -   X is a halogen; and    -   n is 1 or 2.

Suitably, M is a Group I metal. Suitably M is sodium.

Suitably, X is bromine or chlorine. Suitably, X is chlorine.

Suitably n is 1.

Suitably, compound (b) is NaClO₂.

Suitably, the method comprises treating an aqueous system to inhibitgrowth of anaerobic bacteria and/or to reduce the number of liveanaerobic bacteria therein. Suitably, the method comprises treating anaqueous system to inhibit growth of facultative anaerobic bacteriaand/or to reduce the number of live facultative anaerobic bacteriatherein. Suitably, the method comprises treating an aqueous system toinhibit growth of aerobic bacteria and/or to reduce the number of liveaerobic bacteria therein.

Suitably, the aqueous system comprises a mixture of water and otherconstituents. The aqueous system may contain oil. The aqueous system maycomprise an oil and water emulsion. The aqueous system may comprisesolids. The aqueous system may comprise suspended solids. The aqueoussystem may comprise high levels of dissolved solids. The aqueous systemmay comprise one or more salts, for example sodium chloride. Suitably,the aqueous system consists of a body of water. Suitably, the aqueoussystem consists of a body of water which comprises water and otherconstituents, for example dissolved solids.

Suitably, the aqueous system comprises an industrial water system. Theaqueous system may consist of industrial water. The aqueous system mayconsist of industrial water which may comprise water and otherconstituents. The aqueous system may comprise a cooling water system.The aqueous system may consist of cooling water which may comprise waterand other constituents. The aqueous system may comprise a pulping andpapermaking system. The aqueous system may consist of pulping andpapermaking water which may comprise water and other constituents. Theaqueous system may comprise an oil and gas field water system. Theaqueous system may consist of oil and gas field water which may comprisewater and other constituents. The aqueous system may comprise a welltreatment fluid. The aqueous system may consist of well treatment fluidwhich may comprise water and other constituents.

Suitably, the method comprises treating industrial water to inhibitgrowth of one or more micro-organisms therein and/or to reduce thenumber of live micro-organisms therein, wherein the method comprisesadding treatment agents to said industrial water. The method maycomprise treating cooling water to inhibit growth of one or moremicro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to said cooling water. The method may comprise treating pulpingand papermaking water to inhibit growth of one or more micro-organismstherein and/or to reduce the number of live micro-organisms therein,wherein the method comprises adding treatment agents to said pulping andpapermaking water. The method may comprise treating oil and gas fieldwater to inhibit growth of one or more micro-organisms therein and/or toreduce the number of live micro-organisms therein, wherein the methodcomprises adding treatment agents to said oil and gas field water. Themethod may comprise treating a well treatment fluid to inhibit growth ofone or more micro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to well treatment fluid.

Suitably, the method comprises treating an aqueous system whichcomprises water in an amount of up to 99% by weight. Suitably, themethod comprises treating an aqueous system which comprises water in anamount of up to 98% by weight. Suitably, the method comprises treatingan aqueous system which comprises water in an amount of up to 97% byweight. Suitably, the method comprises treating an aqueous system whichcomprises water in an amount of up to 96% by weight. Suitably, themethod comprises treating an aqueous system which comprises water in anamount of up to 95% by weight.

Suitably, the method comprises treating an aqueous system whichcomprises water and one or more constituents comprising organic liquids,organic solids and/or inorganic solids.

Suitably, the method comprises treating an aqueous system whichcomprises water and oil. Suitably, the aqueous system comprises oil inan amount of at least 1% by weight, for example at least 2% by weight.

Suitably, the method comprises treating an aqueous system whichcomprises water and dissolved solids. Suitably, the aqueous systemcomprises dissolved solids in an amount of at least 1% by weight, forexample at least 2% by weight.

Suitably, the method comprises treating an aqueous system whichcomprises water and dissolved organic solids. Suitably, the aqueoussystem comprises dissolved organic solids in an amount of at least 1% byweight, for example at least 2% by weight.

Suitably, the method comprises treating an aqueous system whichcomprises water and dissolved inorganic solids. Suitably, the aqueoussystem comprises dissolved inorganic solids, for example salts, in anamount of at least 1% by weight, for example at least 2% by weight.

Suitably, the method comprises treating an aqueous system whichcomprises dissolved solids.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 1000 mg l⁻¹ or greater. Suitably, the aqueoussystem has a total dissolved solids (TDS) of at least 2000 mg l⁻¹, forexample at least: 3000 mg l⁻¹; 4000 mg l⁻¹; 5000 mg l⁻¹; 6000 mg l⁻¹;7000 mg l⁻¹; 8000 mg l⁻¹; or 9000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 10,000 mg l⁻¹ or greater. Suitably, theaqueous system has a total dissolved solids (TDS) of at least 11,000 mgl⁻¹, for example at least: 12,000 mg l⁻¹; 13,000 mg l⁻¹; 14,000 mg l⁻¹;15,000 mg l⁻¹; 16,000 mg l⁻¹; 17,000 mg l⁻¹; 18,000 mg l⁻¹; or 19,000 mgl⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 20,000 mg l⁻¹ or greater. Suitably, theaqueous system has a total dissolved solids (TDS) of at least 21,000 mgl⁻¹, for example at least: 22,000 mg l⁻¹; 23,000 mg l⁻¹; 24,000 mg l⁻¹;25,000 mg l⁻¹; 26,000 mg l⁻¹; 27,000 mg l⁻¹; 28,000 mg l⁻¹; or 29,000 mgl⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 30,000 mg l⁻¹ or greater. Suitably, theaqueous system has a total dissolved solids (TDS) of at least 31,000 mgl⁻¹, for example at least: 32,000 mg l⁻¹; for example at least: 33,000mg l⁻¹; 34,000 mg l⁻¹; 35,000 mg l⁻¹; 36,000 mg l⁻¹; 37,000 mg l⁻¹;38,000 mg l⁻¹; 39,000 mg l⁻¹; or 40,000 mg l⁻¹.

The method may comprise treating an aqueous system having a totaldissolved solids (TDS) of 50,000 mg l⁻¹ or greater. The aqueous systemmay have a total dissolved solids (TDS) of at least 60,000 mg l⁻¹, forexample at least: 70,000 mg l⁻¹; 80,000 mg l⁻¹; 90,000 mg l⁻¹; 100,000mg l⁻¹; 110,000 mg l⁻¹; 120,000 mg l⁻¹; 130,000 mg l⁻¹; 140,000 mg l⁻¹;150,000 mg l⁻¹; 160,000 mg l⁻¹; 170,000 mg l⁻¹; 180,000 mg l⁻¹; 190,000mg l⁻¹; 200,000 mg l⁻¹; 210,000 mg l⁻¹; 220,000 mg l⁻¹; 230,000 mg l⁻¹;240,000 mg l⁻¹; or 250,000 mg l⁻¹; 260,000 mg l⁻¹; 270,000 mg l⁻¹;280,000 mg l⁻¹; 290,000 mg l⁻¹; 300,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 250,000 mg l⁻¹ or less. The aqueous system mayhave a total dissolved solids (TDS) of no more than 240,000 mg l⁻¹, forexample no more than 230,000 mg l⁻¹; 220,000 mg l⁻¹; 210,000 mg l⁻¹;200,000 mg l⁻¹; 190,000 mg l⁻¹; 180,000 mg l⁻¹; 170,000 mg l⁻¹; 160,000mg l⁻¹; 150,000 mg l⁻¹; 140,000 mg l⁻¹; 130,000 mg l⁻¹; 120,000 mg l⁻¹;or 110,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 100,000 mg l⁻¹ or less. The aqueous system mayhave a total dissolved solids (TDS) of no more than 90,000 mg l⁻¹, forexample no more than 80,000 mg l⁻¹; 70,000 mg l⁻¹; 60,000 mg l⁻¹; 50,000mg l⁻¹; or 40,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of at least 25,000 mg l⁻¹. Suitably, the methodcomprises treating an aqueous system having a total dissolved solids(TDS) of at least 30,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of from 10,000 mg l⁻¹ to 300,000 mg l⁻¹.Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of from 10,000 mg l⁻¹ to 100,000 mg l⁻¹.Suitably, the aqueous system has a total dissolved solids (TDS) of from20,000 mg l⁻¹ to 100,000 mg l⁻¹, for example from 25,000 mg l⁻¹ to100,000 mg l⁻¹. Suitably, the aqueous system has a total dissolvedsolids (TDS) of from 30,000 mg l⁻¹ to 100,000 mg l⁻¹. Suitably, themethod comprises treating an aqueous system having a total dissolvedsolids (TDS) of from 20,000 mg l⁻¹ to 80,000 mg l⁻¹, for example from25,000 mg l⁻¹ to 80,000 mg l⁻¹. Suitably, the method comprises treatingan aqueous system having a total dissolved solids (TDS) of from 30,000mg l⁻¹ to 80,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system comprisingdissolved salts in an amount of 1000 mg l⁻¹ or greater. Suitably, theaqueous system comprises dissolved salts in an amount of at least 2000mg l⁻¹, for example at least: 3000 mg l⁻¹; 4000 mg l⁻¹; 5000 mg l⁻¹;6000 mg l⁻¹; 7000 mg l⁻¹; 8000 mg l⁻¹; or 9000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system comprisingdissolved salts in an amount 10,000 mg l⁻¹ or greater. Suitably, theaqueous system comprises dissolved salts in an amount of at least 11,000mg l⁻¹, for example at least: 12,000 mg l⁻¹; 13,000 mg l⁻¹; 14,000 mgl⁻¹; 15,000 mg l⁻¹; 16,000 mg l⁻¹; 17,000 mg l⁻¹; 18,000 mg l⁻¹; or19,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system comprisingdissolved salts in an amount of 20,000 mg l⁻¹ or greater. Suitably, theaqueous system comprises dissolved salts in an amount of at least 21,000mg l⁻¹, for example at least: 22,000 mg l⁻¹; 23,000 mg l⁻¹; 24,000 mgl⁻¹; 25,000 mg l⁻¹; 26,000 mg l⁻¹; 27,000 mg l⁻¹; 28,000 mg l⁻¹; or29,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system comprisingdissolved salts in an amount of 30,000 mg l⁻¹ or greater. Suitably, theaqueous system comprises dissolved salts in an amount of at least 31,000mg l⁻¹, for example at least: 32,000 mg l⁻¹; for example at least:33,000 mg l⁻¹; 34,000 mg l⁻¹; 35,000 mg l⁻¹; 36,000 mg l⁻¹; 37,000 mgl⁻¹; 38,000 mg l⁻¹; 39,000 mg l⁻¹; or 40,000 mg l⁻¹.

The method may comprise treating an aqueous system comprising dissolvedsalts in an amount of 50,000 mg l⁻¹ or greater. The aqueous system maycomprise dissolved salts in an amount of at least 60,000 mg l⁻¹, forexample at least: 70,000 mg l⁻¹; 80,000 mg l⁻¹; 90,000 mg l⁻¹; 100,000mg l⁻¹; 110,000 mg l⁻¹; 120,000 mg l⁻¹; 130,000 mg l⁻¹; 140,000 mg l⁻¹;150,000 mg l⁻¹; 160,000 mg l⁻¹; 170,000 mg l⁻¹; 180,000 mg l⁻¹; 190,000mg l⁻¹; 200,000 mg l⁻¹; 210,000 mg l⁻¹; 220,000 mg l⁻¹; 230,000 mg l⁻¹;240,000 mg l⁻¹; or 250,000 mg l⁻¹; 260,000 mg l⁻¹; 270,000 mg l⁻¹;280,000 mg l⁻¹; 290,000 mg l⁻¹; 300,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system comprisingdissolved salts in an amount of 250,000 mg l⁻¹ or less. The aqueoussystem may comprise dissolved salts in an amount of no more than 240,000mg l⁻¹, for example no more than 230,000 mg l⁻¹; 220,000 mg l⁻¹; 210,000mg l⁻¹; 200,000 mg l⁻¹; 190,000 mg l⁻¹; 180,000 mg l⁻¹; 170,000 mg l⁻¹;160,000 mg l⁻¹; 150,000 mg l⁻¹; 140,000 mg l⁻¹; 130,000 mg l⁻¹; 120,000mg l⁻¹; or 110,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system comprisingsalts in an amount of 100,000 mg l⁻¹ or less. The aqueous system maycomprise salts in an amount of no more than 90,000 mg l⁻¹, for exampleno more than 80,000 mg l⁻¹; 70,000 mg l⁻¹; 60,000 mg l⁻¹; 50,000 mg l⁻¹;or 40,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system comprisingdissolved salts in an amount of at least 25,000 mg l⁻¹. Suitably, themethod comprises treating an aqueous system comprising dissolved saltsin an amount of at least 30,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system comprisingdissolved salts in an amount of from 10,000 mg l⁻¹ to 300,000 mg l⁻¹.Suitably, the method comprises treating an aqueous system comprisingdissolved salts in an amount of from 10,000 mg l⁻¹ to 100,000 mg l⁻¹.Suitably, the aqueous system comprises dissolved salts in an amount offrom 20,000 mg l⁻¹ to 100,000 mg l⁻¹, for example from 25,000 mg l⁻¹ to100,000 mg l⁻¹. Suitably, the aqueous system comprises dissolved saltsin an amount of from 30,000 mg l⁻¹ to 100,000 mg l⁻¹. Suitably, themethod comprises treating an aqueous system comprising dissolved saltsin an amount of from 20,000 mg l⁻¹ to 80,000 mg l⁻¹, for example from25,000 mg l⁻¹ to 80,000 mg l⁻¹. Suitably, the method comprises treatingan aqueous system comprising dissolved salts in an amount of from 30,000mg l⁻¹ to 80,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system to inhibit thegrowth of a plurality of different micro-organisms.

Suitably, the method comprises treating an aqueous system to prevent thegrowth of one or more micro-organisms. Suitably, the method comprisestreating an aqueous system to prevent the growth of a plurality ofdifferent micro-organisms.

Suitably, the method comprises treating an aqueous system to kill one ormore micro-organisms. Suitably, the method comprises treating an aqueoussystem to kill a plurality of different micro-organisms.

Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of one or more micro-organisms therein and/or toreduce the number of live micro-organisms therein, wherein saidmicro-organisms are selected from bacteria, fungi and algae. Suitably,the method comprises a method of inhibiting growth of bacteria and/orkilling bacteria. Suitably, the method comprises a method of inhibitinggrowth of fungi and/or killing fungi. Suitably, the method comprises amethod of inhibiting growth of algae and/or killing algae.

Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of anaerobic micro-organisms. Suitably, the methodcomprises treating an aqueous system to kill anaerobic micro-organisms.Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of anaerobic bacteria. Suitably, the method comprisestreating an aqueous system to kill anaerobic bacteria. Suitably, themethod comprises treating an aqueous system to inhibit or prevent thegrowth of facultative anaerobic bacteria. Suitably, the method comprisestreating an aqueous system to kill facultative anaerobic bacteria.

Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of facultative anaerobic bacteria and anaerobicbacteria. Suitably, the method comprises treating an aqueous system tokill facultative anaerobic bacteria and anaerobic bacteria.

Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of aerobic micro-organisms. Suitably, the methodcomprises treating an aqueous system to kill aerobic micro-organisms.Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of aerobic bacteria. Suitably, the method comprisestreating an aqueous system to kill aerobic bacteria.

Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of anaerobic and aerobic micro-organisms. Suitably,the method comprises treating an aqueous system to kill anaerobic andaerobic micro-organisms. Suitably, the method comprises treating anaqueous system to inhibit or prevent the growth of anaerobic and aerobicbacteria. Suitably, the method comprises treating an aqueous system tokill anaerobic and aerobic bacteria.

The method may comprise a method of inhibiting growth of gram-positiveaerobic bacteria, gram-positive facultative anaerobic bacteria,gram-negative aerobic bacteria, gram-negative facultative anaerobicbacteria, gram-positive anaerobic bacteria and/or gram-negativeanaerobic bacteria. The method may comprise a method of inhibitinggrowth of mold and/or yeast. The method may comprise a method ofinhibiting the growth of blue green algae and/or green algae. Suitably,the method comprises a method of inhibiting the growth of gram-negativeaerobic bacteria, gram-negative facultative anaerobic bacteria,gram-negative anaerobic bacteria, and green algae. Suitably, the methodcomprises inhibiting the growth of Pseudomonas aeruginosa bacteria in anaqueous system. Suitably, the method comprises inhibiting the growth ofEnterobacter aerogenes bacteria in an aqueous system. Suitably, themethod comprises inhibiting the growth of Desulfovibrio vulgarisbacteria in an aqueous system. Suitably, the method comprises inhibitingthe growth of Chlorella vulgaris algae in an aqueous system.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a Log 10 reduction of 1 or greater in afacultative anaerobe culture is obtained after a contact time of 24hours. Suitably, the method comprises obtaining a Log 10 reduction of 2or greater to a facultative anaerobe culture after a contact time of 24hours; for example of 3 or greater; 4 or greater; 5 or greater; or 6 orgreater.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a complete kill of a facultative anaerobeculture is obtained after a contact time of 24 hours.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a Log 10 reduction of 1 or greater in afacultative anaerobe culture is obtained after a contact time of 4hours. Suitably, the method comprises obtaining a Log 10 reduction of 2or greater to a facultative anaerobe culture after a contact time of 4hours; for example of 3 or greater; 4 or greater; 5 or greater; or 6 orgreater.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a complete kill of a facultative anaerobeculture is obtained after a contact time of 4 hours. Suitably, themethod comprises adding compounds (a) and (b) to an aqueous system suchthat a complete kill of a facultative anaerobe culture is obtained aftera contact time of no more than 4 hours.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a Log 10 reduction of 1 or greater in afacultative anaerobe culture is obtained after a contact time of 1 hour.Suitably, the method comprises obtaining a Log 10 reduction of 2 orgreater to a facultative anaerobe culture after a contact time of 1hours; for example of 3 or greater; 4 or greater; 5 or greater; or 6 orgreater.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a complete kill of a facultative anaerobeculture is obtained after a contact time of 1 hour. Suitably, the methodcomprises adding compounds (a) and (b) to an aqueous system such that acomplete kill of a facultative anaerobe culture is obtained after acontact time of no more than 1 hour. Suitably, the method comprisesadding compounds (a) and (b) to an aqueous system such that a completekill of a facultative anaerobe culture is obtained after a contact timeof at least 1 hour.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a complete kill of a facultative anaerobeculture is obtained after a contact time of between 1 and 4 hours.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a Log 10 reduction of 1 or greater in ananaerobe culture is obtained after a contact time of 24 hours. Suitably,the method comprises obtaining a Log 10 reduction of 2 or greater to ananaerobe culture after a contact time of 24 hours; for example of 3 orgreater; 4 or greater; or 5 or greater.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a complete kill of an anaerobe culture isobtained after a contact time of 24 hours.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a Log 10 reduction of 1 or greater in ananaerobe culture is obtained after a contact time of 4 hours. Suitably,the method comprises obtaining a Log 10 reduction of 2 or greater to ananaerobe culture after a contact time of 4 hours; for example of 3 orgreater; 4 or greater; or 5 or greater.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a complete kill of an anaerobe culture isobtained after a contact time of 4 hours.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a Log 10 reduction of 1 or greater in ananaerobe culture is obtained after a contact time of 1 hour. Suitably,the method comprises obtaining a Log 10 reduction of 2 or greater to ananaerobe culture after a contact time of 1 hours; for example of 3 orgreater; 4 or greater; or 5 or greater.

Suitably, the method comprises adding compounds (a) and (b) to anaqueous system such that a complete kill of an anaerobe culture isobtained after a contact time of 1 hour. Suitably, the method comprisesadding compounds (a) and (b) to an aqueous system such that a completekill of a facultative anaerobe culture is obtained after a contact timeof at least 1 hour. Suitably, the method comprises adding compounds (a)and (b) to an aqueous system such that a complete kill of anaerobeculture is obtained after a contact time of no more than 1 hour.

The method may comprise adding compounds (a) and (b) to an aqueoussystem such that a Log 10 reduction of 1 or greater in an aerobe cultureis obtained after a contact time of 24 hours. The method may compriseobtaining a Log 10 reduction of 2 or greater to an aerobe culture aftera contact time of 24 hours; for example of 3 or greater; 4 or greater; 5or greater.

The method may comprise adding compounds (a) and (b) to an aqueoussystem such that a Log 10 reduction of 1 or greater in an aerobe cultureis obtained after a contact time of 4 hours. The method may compriseobtaining a Log 10 reduction of 2 or greater to an aerobe culture aftera contact time of 4 hours; for example of 3 or greater; 4 or greater; 5or greater.

The method may comprise adding compounds (a) and (b) to an aqueoussystem such that a Log 10 reduction of 1 or greater in an aerobe cultureis obtained after a contact time of 1 hour. The method may compriseobtaining a Log 10 reduction of 2 or greater to an aerobe culture aftera contact time of 1 hour; for example of 3 or greater; 4 or greater; 5or greater.

Suitably, the method comprises adding compound (a) and compound (b) tothe aqueous system such that they are added in a combined amount of from0.1 to 1000 parts by weight per one million parts by weight of saidaqueous system (ppm), for example from 1 to 500 ppm. Suitably, themethod comprises adding compound (a) and compound (b) to the aqueoussystem in a combined amount of from 0.1 to 300 ppm.

Suitably, the method comprises adding compound (a) and compound (b) tothe aqueous system such that they are present in a combined amount offrom 0.1 to 1000 parts by weight per one million parts by weight of saidaqueous system (ppm), for example from 1 to 500 ppm. Suitably, themethod comprises adding compound (a) and compound (b) to the aqueoussystem such that they are present in a combined amount of from 0.1 to300 ppm.

As used herein, all references to ppm refer to parts per million byweight unless stated otherwise.

Suitably, the method comprises adding compound (a) and compound (b) tothe aqueous system such that they are added in a total amount of from 5to 500 ppm. Suitably, the method comprises adding compound (a) andcompound (b) to the aqueous system such that they are added in a totalamount of from 10 to 400 ppm. Suitably, the method comprises addingcompound (a) and compound (b) to the aqueous system such that they areadded in a total amount of from 15 to 400 ppm, for example 15 to 50 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent (a) to an aqueous system in an amount of at least 0.1 parts permillion (ppm).

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said phosphonium compound in an amount of at least 0.1 partsper million (ppm).

Suitably, the method comprises adding a phosphonium compound to anaqueous system such that it is added in an amount of at least 0.2 ppm.Suitably, the method comprises adding a phosphonium compound to anaqueous system such that it is added in an amount of at least 0.3 ppm,for example at least: 0.4 ppm; 0.5 ppm; 0.6 ppm; 0.7 ppm; 0.8 ppm; 0.9ppm; or 1.0 ppm. Suitably, the method comprises adding a phosphoniumcompound to an aqueous system such that it is added in an amount of atleast 1 ppm; for example at least 1.5 ppm; 2.0 ppm; 2.5 ppm; 3.0 ppm;3.5 ppm; 4.0 ppm; 4.5 ppm; 5.0 ppm; 5.5 ppm; or 6.0 ppm. The method maycomprise adding a phosphonium compound to an aqueous system such that itis added in an amount of at least 6 ppm, for example at least: 7 ppm; 8ppm; 9 ppm; 10 ppm; 11 ppm; 12 ppm. The method may comprise adding aphosphonium compound to an aqueous system such that it is added in anamount of at least 20 ppm, for example at least: 25 ppm; 30 ppm; 35 ppm;40 ppm; 45 ppm; or 50 ppm.

Suitably, the method comprises adding a phosphonium compound to anaqueous system such that it is present in an active amount of at least0.2 ppm. Suitably, the method comprises adding a phosphonium compound toan aqueous system such that it is present in an active amount of atleast 0.3 ppm, for example at least: 0.4 ppm; 0.5 ppm; 0.6 ppm; 0.7 ppm;0.8 ppm; 0.9 ppm; or 1.0 ppm. Suitably, the method comprises adding aphosphonium compound to an aqueous system such that it is present in anactive amount of at least 1 ppm; for example at least 1.5 ppm; 2.0 ppm;2.5 ppm; 3.0 ppm; 3.5 ppm; 4.0 ppm; 4.5 ppm; 5.0 ppm; 5.5 ppm; or 6.0ppm. The method may comprise adding a phosphonium compound to an aqueoussystem such that it is present in an active amount of at least 6 ppm,for example at least: 7 ppm; 8 ppm; 9 ppm; 10 ppm; 11 ppm; 12 ppm. Themethod may comprise adding a phosphonium compound to an aqueous systemsuch that it is present in an active amount of at least 20 ppm, forexample at least: 25 ppm; 30 ppm; 35 ppm; 40 ppm; 45 ppm; or 50 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said phosphonium compound added in an amount of 1 to 20 ppm,for example 1 to 15 ppm. Suitably, the method comprises adding aphosphonium compound treatment agent to an aqueous system to provide atreated aqueous system comprising said phosphonium compound added in anamount of 1 to 10 ppm, for example 2 to 8 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system in an amount of not more than 250 ppm, forexample not more than 125 ppm.

Suitably, the method may comprise adding a phosphonium compoundtreatment agent to an aqueous system in an amount of not more than 100ppm, for example not more than 50 ppm. Suitably, the method comprisesadding a phosphonium compound to an aqueous system such that it is addedin an amount of not more than 40 ppm, for example not more than 35 ppm.The method may comprise adding a phosphonium compound to an aqueoussystem such that it is added in an amount of not more than 30 ppm, forexample not more than 25 ppm. The method may comprise adding aphosphonium compound to an aqueous system such that it is added in anamount of not more than 20 ppm; for example not more than: 15 ppm; 10ppm or 5 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said phosphonium compound in an active amount of not morethan 250 ppm, for example not more than 125 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said phosphonium compound in an active amount of not morethan 100 ppm, for example not more than 50 ppm.

Suitably, the method comprises adding a phosphonium compound to anaqueous system such that it is present in an active amount of not morethan 40 ppm, for example not more than 35 ppm. The method may compriseadding a phosphonium compound to an aqueous system such that it ispresent in an amount of not more than 30 ppm, for example not more than;25 ppm. The method may comprise adding a phosphonium compound to anaqueous system such that it is present in an amount of not more than 20ppm, for example not more than: 15 ppm; 10 ppm; or 5 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said phosphonium compound added in an amount of 5.5 to 7.0ppm, for example 6.0 to 6.5 ppm, for example 6.25 ppm. Suitably, themethod comprises adding a phosphonium compound treatment agent to anaqueous system to provide a treated aqueous system comprising saidphosphonium compound added in an amount of 10 to 15 ppm, for example 12to 13 ppm, or for example 12.5 ppm.

Suitably, the method comprises adding compound (b) treatment agent to anaqueous system in an amount of at least 0.1 ppm.

Suitably, the method comprises adding compound (b) to an aqueous systemto provide a treated aqueous system comprising said compound (b) in anamount of at least 0.1 ppm.

Suitably, the method comprises adding compound (b) to an aqueous systemsuch that it is added in an amount of at least 0.5 ppm. Suitably, themethod comprises adding compound (b) to an aqueous system such that itis added in an amount of at least 1 ppm, for example at least: 2 ppm; 3ppm; 4 ppm or 5 ppm.

Suitably, the method comprises adding compound (b) to an aqueous systemsuch that it is added in an amount of greater than 5 ppm. Suitably, themethod comprises adding compound (b) to an aqueous system such that itis added in an amount of at least 10 ppm. Suitably, the method comprisesadding compound (b) to an aqueous system such that it is added in anamount of at least: 15 ppm, for example at least: 20 ppm; 25 ppm; 30ppm; 35 ppm or 40 ppm. The method may comprise adding compound (b) to anaqueous system such that it is added in an amount of at least 50 ppm,for example at least: 60 ppm; 70 ppm; 80 ppm; 90 ppm or 100 ppm. Themethod may comprise adding compound (b) to an aqueous system such thatit is added in an amount of at least 150 ppm, for example at least: 200ppm; 250 ppm; or 300 ppm.

Suitably, the method comprises adding compound (b) to an aqueous systemsuch that it is present in an amount of at least 0.5 ppm. Suitably, themethod comprises adding compound (b) to an aqueous system such that itis present in an amount of at least 1 ppm, for example at least: 2 ppm;3 ppm; 4 ppm or 5 ppm.

Suitably, the method comprises adding compound (b) to an aqueous systemsuch that it is present in an amount of greater than 5 ppm. Suitably,the method comprises adding compound (b) to an aqueous system such thatit is present in an amount of at least 10 ppm. Suitably, the methodcomprises adding compound (b) to an aqueous system such that it ispresent in an amount of at least: 15 ppm, for example at least: 20 ppm;25 ppm; 30 ppm; 35 ppm or 40 ppm. The method may comprise addingcompound (b) to an aqueous system such that it is present in an amountof at least 50 ppm, for example at least: 60 ppm; 70 ppm; 80 ppm; 90 ppmor 100 ppm. The method may comprise adding compound (b) to an aqueoussystem such that it is present in an amount of at least 150 ppm, forexample at least: 200 ppm; 250 ppm; or 300 ppm.

Suitably, the method comprises adding compound (b) to an aqueous systemsuch that it is added in an amount of not more than 500 ppm. Suitably,the method comprises adding compound (b) to an aqueous system such thatit is added in an amount of not more than 400 ppm; for example not morethan 300 ppm. The method may comprise adding compound (b) to an aqueoussystem such that it is added in an amount of not more than 200 ppm, forexample not more than 100 ppm.

Suitably, the method comprises adding compound (b) to an aqueous systemsuch that it is present in an amount of not more than 500 ppm. Suitably,the method comprises adding compound (b) to an aqueous system such thatit is present in an amount of not more than 400 ppm; for example notmore than 300 ppm. The method may comprise adding compound (b) to anaqueous system such that it is present in an amount of not more than 200ppm, for example not more than 100 ppm.

Suitably, the method comprises adding compound (b) to an aqueous systemto provide a treated aqueous system comprising compound (b) in an amountof 1 to 500 ppm, for example 5 to 400 ppm. The method may compriseadding compound (b) to an aqueous system to provide a treated aqueoussystem comprising compound (b) in an amount of 10 to 300 ppm, forexample 10 to 100 ppm.

Suitably, the method comprises adding NaClO₂ treatment agent to anaqueous system in an amount of at least 0.1 ppm.

Suitably, the method comprises adding NaClO₂ to an aqueous system toprovide a treated aqueous system comprising said NaClO₂ in an amount ofat least 0.1 ppm.

Suitably, the method comprises adding NaClO₂ to an aqueous system suchthat it is added in an amount of at least 0.5 ppm. Suitably, the methodcomprises adding NaClO₂ to an aqueous system such that it is added in anamount of at least 1 ppm, for example at least: 2 ppm; 3 ppm; 4 ppm or 5ppm.

Suitably, the method comprises adding NaClO₂ to an aqueous system suchthat it is added in an amount of greater than 5 ppm. Suitably, themethod comprises adding NaClO₂ to an aqueous system such that it isadded in an amount of at least 10 ppm. Suitably, the method comprisesadding NaClO₂ to an aqueous system such that it is added in an amount ofat least: 15 ppm, for example at least: 20 ppm; 25 ppm; 30 ppm; 35 ppmor 40 ppm. The method may comprise adding NaClO₂ to an aqueous systemsuch that it is added in an amount of at least 50 ppm, for example atleast: 60 ppm; 70 ppm; 80 ppm; 90 ppm or 100 ppm. The method maycomprise adding NaClO₂ to an aqueous system such that it is added in anamount of at least 150 ppm, for example at least: 200 ppm; 250 ppm; or300 ppm.

Suitably, the method comprises adding NaClO₂ to an aqueous system suchthat it is present in an amount of at least 0.5 ppm. Suitably, themethod comprises adding NaClO₂ to an aqueous system such that it ispresent in an amount of at least 1 ppm, for example at least: 2 ppm; 3ppm; 4 ppm or 5 ppm.

Suitably, the method comprises adding NaClO₂ to an aqueous system suchthat it is present in an amount of greater than 5 ppm. Suitably, themethod comprises adding NaClO₂ to an aqueous system such that it ispresent in an amount of at least 10 ppm. Suitably, the method comprisesadding NaClO₂ to an aqueous system such that it is present in an amountof at least: 15 ppm, for example at least: 20 ppm; 25 ppm; 30 ppm; 35ppm or 40 ppm. The method may comprise adding NaClO₂ to an aqueoussystem such that it is present in an amount of at least 50 ppm, forexample at least: 60 ppm; 70 ppm; 80 ppm; 90 ppm or 100 ppm. The methodmay comprise adding NaClO₂ to an aqueous system such that it is presentin an amount of at least 150 ppm, for example at least: 200 ppm; 250ppm; or 300 ppm.

Suitably, the method comprises adding NaClO₂ to an aqueous system suchthat it is added in an amount of not more than 500 ppm. Suitably, themethod comprises adding NaClO₂ to an aqueous system such that it isadded in an amount of not more than 400 ppm; for example not more than300 ppm. The method may comprise adding NaClO₂ to an aqueous system suchthat it is added in an amount of not more than 200 ppm, for example notmore than 100 ppm.

Suitably, the method comprises adding NaClO₂ to an aqueous system suchthat it is present in an amount of not more than 500 ppm. Suitably, themethod comprises adding NaClO₂ to an aqueous system such that it ispresent in an amount of not more than 400 ppm; for example not more than300 ppm. The method may comprise adding NaClO₂ to an aqueous system suchthat it is present in an amount of not more than 200 ppm, for examplenot more than 100 ppm.

Suitably, the method comprises adding NaClO₂ to an aqueous system toprovide a treated aqueous system comprising NaClO₂ in an amount of 1 to500 ppm, for example 5 to 400 ppm. The method may comprise adding NaClO₂to an aqueous system to provide a treated aqueous system comprisingNaClO₂ in an amount of 10 to 300 ppm, for example 10 to 100 ppm.

Suitably the method comprises adding compound (a) and compound (b) to anaqueous system in a weight ratio of compound (a):compound (b) of from10:1 to 1:60, for example from 5:1 to 1:50.

The method may comprise adding compound (a) and compound (b) to anaqueous system in a weight ratio of compound (a):compound (b) of from2:1 to 1:10, for example from 1.5:1.0 to 1.0:5.0.

As used herein, all ratios are weight ratios unless stated otherwise.

Suitably the method comprises adding compound (a) and compound (b) to anaqueous system in a ratio of at least 1:60, for example at least 1:5.

Suitably the method comprises adding compound (a) and compound (b) to anaqueous system in a ratio of no more than 10:1, for example no more than2:1.

Suitably the method comprises adding compound (a) and compound (b) to anaqueous system in a ratio of from 1.0:1.0 to 1.0:2.0, for example1.0:1.5.

Suitably the method comprises adding compound (a) and compound (b) to anaqueous system in a ratio of from 1.0:3.0 to 1.0:4.0, for example1.0:3.3.

Suitably the method comprises adding compound (a) and compound (b) to anaqueous system in a ratio of from 1.0:1.0 to 2.0:1.0, for example1.3:1.0.

Suitably the method comprises adding compound (a) and compound (b) to anaqueous system in a ratio of from 1.0:1.0 to 1.0:2.0; for example1.0:1.6.

The method may comprise adding a combination of phosphonium compounds(a) to an aqueous system. Suitably, the method comprises adding a singletype of phosphonium compound (a) to an aqueous system.

Suitably, the method employs a phosphonium compound (a) having formula:

wherein each R is independently a C₁-C₆ alkyl group which isunsubstituted or substituted by a cyano, hydroxyl, esterified hydroxylor aryl group;

R¹ represents a C₈-C₁₈ alkyl group which is substituted orunsubstituted; and

X represents either chlorine or bromine.

Suitably, each R is a C₁-C₆ alkyl group. Suitably, each R is a C₃-C₅alkyl group. Suitably each R is a butyl group.

Suitably R¹ represents a C₈-C₁₈ alkyl group. Suitably, R1 is a C₁₂-C₁₆alkyl group. Suitably, R¹ is a tetradecyl group.

Suitably, X is chlorine.

Suitably, the method employs a phosphonium compound (a) which is aphosphonium chloride.

Suitably, the method comprises treating an aqueous system such thatphosphonium chloride comprises greater than 50% of the total phosphoniumcompound(s) added to the aqueous system. Suitably, the method comprisestreating an aqueous system such that phosphonium chloride comprisesgreater than 90% of the total phosphonium compound(s) added to theaqueous system, for example 99% or greater.

Suitably, the method comprises treating an aqueous system such thatphosphonium chloride comprises greater than 50% of the total phosphoniumcompound(s) present in the aqueous system. Suitably, the methodcomprises treating an aqueous system such that phosphonium chloridecomprises greater than 90% of the total phosphonium compound(s) presentin the aqueous system, for example 99% or greater.

Suitably, the method employs a phosphonium chloride as the onlyphosphonium compound (a).

Suitably, the method comprises adding tri n-butyl n-tetradecylphosphonium chloride (hereafter “TTPC”) to the aqueous system. Suitably,the phosphonium compound (a) is TTPC.

Suitably, the method comprises adding TTPC to an aqueous system in anamount of at least 0.1 parts per million (ppm).

Suitably, the method comprises adding TTPC to an aqueous system toprovide a treated aqueous system comprising TTPC in an amount of atleast 0.1 parts per million (ppm).

Suitably, the method comprises adding TTPC to an aqueous system suchthat it is added in an amount of at least 0.2 ppm. Suitably, the methodcomprises adding TTPC to an aqueous system such that it is added in anamount of at least 0.3 ppm, for example at least: 0.4 ppm; 0.5 ppm; 0.6ppm; 0.7 ppm; 0.8 ppm; 0.9 ppm; or 1.0 ppm. Suitably, the methodcomprises adding TTPC to an aqueous system such that it is added in anamount of at least 1 ppm; for example at least 1.5 ppm; 2.0 ppm; 2.5ppm; 3.0 ppm; 3.5 ppm; 4.0 ppm; 4.5 ppm; 5.0 ppm; 5.5 ppm; or 6.0 ppm.The method may comprise adding TTPC to an aqueous system such that it isadded in an amount of at least 6 ppm, for example at least: 7 ppm; 8ppm; 9 ppm; 10 ppm; 11 ppm; 12 ppm. The method may comprise adding TTPCto an aqueous system such that it is added in an amount of at least 20ppm, for example at least: 25 ppm; 30 ppm; 35 ppm; 40 ppm; 45 ppm; or 50ppm.

Suitably, the method comprises adding TTPC to an aqueous system suchthat it is present in an active amount of at least 0.2 ppm. Suitably,the method comprises adding TTPC to an aqueous system such that it ispresent in an active amount of at least 0.3 ppm, for example at least:0.4 ppm; 0.5 ppm; 0.6 ppm; 0.7 ppm; 0.8 ppm; 0.9 ppm; or 1.0 ppm.Suitably, the method comprises adding TTPC to an aqueous system suchthat it is present in an active amount of at least 1 ppm; for example atleast 1.5 ppm; 2.0 ppm; 2.5 ppm; 3.0 ppm; 3.5 ppm; 4.0 ppm; 4.5 ppm; 5.0ppm; 5.5 ppm; or 6.0 ppm. The method may comprise adding a TTPC to anaqueous system such that it is present in an active amount of at least 6ppm, for example at least: 7 ppm; 8 ppm; 9 ppm; 10 ppm; 11 ppm; 12 ppm.The method may comprise adding TTPC to an aqueous system such that it ispresent in an active amount of at least 20 ppm, for example at least: 25ppm; 30 ppm; 35 ppm; 40 ppm; 45 ppm; or 50 ppm.

Suitably, the method comprises adding TTPC to an aqueous system toprovide a treated aqueous system comprising TTPC in an amount of 1 to 20ppm, for example 1 to 15 ppm. Suitably, the method comprises adding TTPCto an aqueous system to provide a treated aqueous system comprising TTPCin an amount of 1 to 10 ppm, for example 2 to 8 ppm, for example 5 to 7ppm. Suitably, the method comprises adding TTPC to an aqueous system toprovide a treated aqueous system comprising TTPC in an amount of 5 to 15ppm, for example 10 to 14 ppm, for example 11 to 13 ppm.

Suitably, the method comprises adding TTPC to an aqueous system in anamount of not more than 250 ppm, for example not more than 125 ppm.

Suitably, the method may comprise adding TTPC to an aqueous system in anamount of not more than 100 ppm, for example not more than 50 ppm.Suitably, the method comprises adding TTPC to an aqueous system suchthat it is added in an amount of not more than 40 ppm, for example notmore than 35 ppm. The method may comprise adding TTPC to an aqueoussystem such that it is added in an amount of not more than 30 ppm, forexample not more than; 25 ppm; 20 ppm. The method may comprise addingTTPC to an aqueous system such that it is added in an amount of not morethan 15 ppm, for example not more than 10 ppm.

Suitably, the method comprises adding TTPC to an aqueous system toprovide a treated aqueous system comprising TTPC in an active amount ofnot more than 250 ppm, for example not more than 125 ppm.

Suitably, the method comprises adding TTPC to an aqueous system toprovide a treated aqueous system comprising TTPC in an active amount ofnot more than 100 ppm, for example not more than 50 ppm. Suitably, themethod comprises adding TTPC to an aqueous system such that it ispresent in an active amount of not more than 40 ppm, for example notmore than 35 ppm. The method may comprise adding a TTPC to an aqueoussystem such that it is present in an amount of not more than 30 ppm, forexample not more than; 25 ppm; 20 ppm; 15 ppm; 10 ppm; or 5 ppm.

Suitably, the method comprises adding TTPC to an aqueous system toprovide a treated aqueous system comprising TTPC in an amount of 5.5 to7.0 ppm, for example 6.0 to 6.5 ppm, for example 6.25 ppm. Suitably, themethod comprises adding TTPC to an aqueous system to provide a treatedaqueous system comprising TTPC in an amount of 10 to 15 ppm, for example12 to 13 ppm for example 12.5 ppm.

Suitably, the method comprises adding an aqueous composition containingthe phosphonium compound (a) to the aqueous system. Suitably, the methodcomprises adding an aqueous composition of TTPC to the aqueous system.The method may comprise adding an aqueous composition comprising 5% byweight of TTPC to the aqueous system. A suitable composition containingTTPC is available from BWA Water Additives and is sold under the tradename Bellacide 355 (an aqueous composition of TTPC and water consistingof water and 5% by weight of TTPC). The method may comprise adding anaqueous composition comprising 50% by weight of TTPC to the aqueoussystem. A suitable composition containing TTPC is available from BWAWater Additives and is sold under the trade name Bellacide 350 (anaqueous composition of TTPC and water consisting of water and 50% byweight of TTPC).

Suitably, the method comprises treating an aqueous system such that TTPCcomprises greater than 50% of the total phosphonium compound(s) added tothe aqueous system. Suitably, the method comprises treating an aqueoussystem such that TTPC comprises greater than 90% of the totalphosphonium compound(s) added to the aqueous system, for example 99% orgreater.

Suitably, the method comprises treating an aqueous system such that TTPCcomprises greater than 50% of the total phosphonium compound(s) presentin the aqueous system. Suitably, the method comprises treating anaqueous system such that TTPC comprises greater than 90% of the totalphosphonium compound(s) present in the aqueous system, for example 99%or greater.

Suitably, the method employs TTPC as the only phosphonium compound (a).

The method may comprise adding a combination of compounds of type (b) toan aqueous system. Suitably, the method comprises adding a singlecompound of type (b) to an aqueous system.

Suitably, the method employs NaClO₂ as the only compound of type (b).

Suitably, the method comprises treating an aqueous system such thatNaClO₂ comprises greater than 50% of the compounds of type (b) added tothe aqueous system. Suitably, the method comprises treating an aqueoussystem such that NaClO₂ comprises greater than 90% of the total ofcompounds of type (b) added to the aqueous system, for example 99% orgreater.

Suitably, the method employs a beneficial combination of compounds (a)and (b). The method may employ a synergistic mixture of compounds (a)and (b). Suitably, by “synergistic mixture” it is meant that the mixtureof compounds (a) and (b) has a synergistic effect on the inhibition ofgrowth of one or more biological organisms, preferably micro-organismssuch as bacteria, fungi and/or algae and/or has a synergistic effect onreducing the number of one or more biological organisms, preferablymicro-organisms such as bacteria, fungi and/or algae.

Suitably the method comprises adding TTPC and NaClO₂ to an aqueoussystem in a weight ratio of TTPC:NaClO₂ of from 10:1 to 1:60, forexample from 5:1 to 1:50.

The method may comprise adding TTPC and NaClO₂ to an aqueous system in aweight ratio of TTPC:NaClO₂ of from 2:1 to 1:10, for example from1.5:1.0 to 1.0:5.0.

Suitably, the method comprises adding TTPC and NaClO₂ to an aqueoussystem such that TTPC is added in an amount of 20 ppm or less and suchthat TTPC and NaClO₂ are added in a weight ratio of TTPC:NaClO₂ of from2:1 to 1:10.

Suitably, the method comprises adding TTPC and NaClO₂ to an aqueoussystem such that TTPC is added in an amount of 15 ppm or less and suchthat TTPC and NaClO₂ are added in a weight ratio of TTPC:NaClO₂ of from2:1 to 1:10.

Suitably, the method comprises adding TTPC and NaClO₂ to an aqueoussystem such that TTPC is added in an amount of 10 ppm or less and suchthat TTPC and NaClO₂ are added in a weight ratio of TTPC:NaClO₂ of from2:1 to 1:10.

Suitably, the method comprises adding TTPC and NaClO₂ to an aqueoussystem such that TTPC is added in an amount of 1 to 8 ppm and such thatTTPC and NaClO₂ are added in a weight ratio of TTPC:NaClO₂ of from1.5:1.0 to 1.0:5.0.

Suitably, the method comprises adding TTPC and NaClO₂ to an aqueoussystem such that TTPC is added in an amount of 20 ppm or less and suchthat TTPC and NaClO₂ are added in a weight ratio of TTPC:NaClO₂ of from2:1 to 1:10.

Suitably, the method comprises treating an oil and gas field watersystem having a total dissolved solids (TDS) of 30,000 mg l⁻¹ or greaterand the method comprises adding TTPC and NaClO₂ such that TTPC is addedin an amount of 20 ppm or less and such that TTPC and NaClO₂ are addedin a weight ratio of TTPC:NaClO₂ of from 2:1 to 1:10.

The method may comprise adding compound (a) and compound (b) to theaqueous system such that the aqueous system comprises a synergisticmixture of compounds (a) and (b).

The method may comprise adding compound (a) and compound (b) as amixture to the aqueous system. The method may comprise adding a biocidalcomposition comprising compound (a) and compound (b) to the aqueoussystem. The method may comprise mixing compound (a) and compound (b) andadding the mixture to the aqueous system. Suitably, the method comprisesadding compound (a) and compound (b) separately to the aqueous systemand allowing or causing them to mix within the aqueous system.

Where the method comprises mixing compound (a) and compound (b) andadding the mixture to the aqueous system and/or adding compound (a) andcompound (b) separately to the aqueous system and allowing or causingthem to mix within the aqueous system, then compounds (a) and (b) arepreferably used in the form of aqueous compositions.

Suitably, compound (a) is used in the form of an aqueous compositioncomprising between 1% and 90% by weight of compound (a), for examplebetween 1% and 60% by weight. Suitably, compound (a) is used in the formof an aqueous composition comprising between 1% and 10% by weight ofcompound (a), for example 5% by weight.

Suitably, compound (b) is used in the form of an aqueous compositioncomprising between 1% and 95% by weight of compound (b), for examplebetween 10% and 90% by weight. Suitably, compound (b) is used in theform of an aqueous composition comprising between 50% and 90% by weightof compound (b), for example 80% by weight.

The method may comprise adding a stabilising agent to the aqueoussystem. The method may comprise adding a stabilised treatment agent tothe aqueous system. The method may comprise adding a treatment agentcomprising compound (a) or (b) and a stabiliser.

The method may comprise a method of treating an industrial water system.The method may comprise treating a cooling water system. The method maycomprise treating a pulping and/or papermaking water system. The methodmay comprise treating an oil and/or gas field water system. The methodmay comprise treating an aqueous system to control the growth ofbacterial and/or algal micro-organisms contained therein and/or whichmay become entrained in said system.

It has been found that the compositions and methods of utilisation ofthe present invention may in particular be efficacious in controllingacid producing facultative anaerobic bacteria and hydrogen sulphideproducing anaerobic bacteria which may populate aqueous systems.

Surprisingly, it has been found that when compound (a) and compound (b)are combined, the resulting combination may pose a higher degree ofbiocidal activity in an aqueous system than that of the individualcompounds used alone. Because of the enhanced activity of thecombination of treatment agent compounds, it may be possible for thetotal quantity of treatment agent added to an aqueous system to bereduced in comparison to a system using only one of said treatment agentcompounds. In addition, the high degree of biocidal activity which isprovided by each of the treatment agent compounds may be exploitedwithout use of higher concentrations of each. The combination of TTPCand NaClO₂ may be particularly effective. The composition may also besurprisingly effective in systems having high total dissolved solids(TDS).

It has been found that the compositions and methods of utilisation ofthe present invention may in particular be efficacious in controllingthe facultative anaerobic bacterium Enterobacter aerogenes and/or theanaerobic bacterium Desulfovibrio vulgaris, which may populate aqueoussystems.

Surprisingly, the present inventors have found that mixtures of compound(a) and compound (b), such as mixtures of tri-n-butyl n-tetradecylphosphonium chloride (TTPC) and NaClO₂, are especially efficacious incontrolling the growth of micro-organisms such as bacterial and algalmicrobes in aqueous systems comprising dissolved solids and there is anunexpected synergistic relationship.

It has been found that compositions of compounds (a) and compound (b)may be unexpectedly effective against facultative anaerobes andanaerobes and may have a marked synergy at short contact times. Forexample, NaClO₂ may show no biocidal activity against anaerobes orfacultative anaerobes at short contact times but the addition of TTPCmay greatly improve performance even though TTPC alone may be of limitedeffectiveness against anaerobes and may be ineffective againstfacultative anaerobes at short contact times.

According to a second aspect of the present invention there is provideda method of treating an aqueous system comprising greater than 20,000 mgl⁻¹ total dissolved solids (TDS) to inhibit growth of one or moremicro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to said aqueous system and wherein said treatment agentscomprise:

(a) TTPC; and

(b) NaClO₂.

The method of the second aspect may comprise any feature as described inrelation to the first aspect except where such features are mutuallyexclusive.

According to a third aspect of the present invention there is providedan aqueous system comprising a combination of:

(a) a phosphonium compound; and

(b) a compound having formula:M(XO₂)_(n)

-   -   wherein:    -   M is a Group I or Group II metal;    -   X is a halogen; and    -   n is 1 or 2.

Suitably, M is a Group I metal. Suitably M is sodium.

Suitably, X is bromine or chlorine. Suitably, X is chlorine.

Suitably n is 1.

Suitably, compound (b) is NaClO₂.

Suitably, the aqueous system comprises greater than 10,000 mg l⁻¹ totaldissolved solids (TDS). Suitably, the aqueous system comprises greaterthan 20,000 mg l⁻¹ total dissolved solids (TDS), for example greaterthan 30,000 mg l⁻¹ TDS.

Suitably, compound (a) is TTPC.

Suitably the aqueous system comprises a mixture of water and otherconstituents. The aqueous system may contain oil. The aqueous system maycomprise an oil and water emulsion. The aqueous system may comprisesolids. The aqueous system may comprise suspended solids. The aqueoussystem may comprise high levels of dissolved solids. The aqueous systemmay comprise one or more salts, for example sodium chloride. Suitably,the aqueous system consists of a body of water. Suitably, the aqueoussystem consists of a body of water which comprises water and otherconstituents, for example dissolved solids.

Suitably, the aqueous system comprises an industrial water system. Theaqueous system may consist of industrial water. The aqueous system maycomprise a cooling water system. The aqueous system may comprise apulping and papermaking system. The aqueous system may comprise an oiland gas field water system. The aqueous system may comprise a welltreatment fluid.

The aqueous system may comprise cooling water. The aqueous system mayconsist of cooling water, comprising compound (a), compound (b) andoptionally other constituents in addition to water. The aqueous systemmay comprise pulping and papermaking water. The aqueous system mayconsist of pulping and papermaking water, comprising compound (a),compound (b) and optionally other constituents in addition to water. Theaqueous system may comprise oil and gas field water. The aqueous systemmay consist of oil and gas field water, comprising compound (a),compound (b) and optionally other constituents in addition to water. Theaqueous system may comprise well treatment fluid. The aqueous system mayconsist of well treatment fluid, comprising compound (a), compound (b)and optionally other constituents in addition to water.

Suitably, the aqueous system comprises TTPC in an amount of 20 ppm orless and comprises TTPC and NaClO₂ in a weight ratio of TTPC:NaClO₂ offrom 10:1 to 1:60, for example 2:1 to 1:10.

Suitably, the aqueous system comprises an oil and gas field water systemhaving a total dissolved solids (TDS) of 30,000 mg l⁻¹ or greater andcomprises TTPC and NaClO₂ such that TTPC is present in an amount of 20ppm or less and such that TTPC and NaClO₂ are present in a weight ratioof TTPC:NaClO₂ of from 2:1 to 1:10.

The aqueous system of the third aspect may comprise any feature asdescribed in relation to one or more of the first and/or second aspectsexcept where such features are mutually exclusive.

According to a fourth aspect of the present invention there is provideda method of inhibiting or preventing the growth of one or moremicro-organisms in a water-based liquid, wherein the method comprisesadding treatment agents to said water-based liquid and wherein saidtreatment agents comprise:

(a) a phosphonium compound; and

(b) a compound having formula:M(XO₂)_(n)

-   -   wherein:    -   M is a Group I or Group II metal;    -   X is a halogen; and    -   n is 1 or 2.

Suitably, M is a Group I metal. Suitably M is sodium.

Suitably, X is bromine or chlorine. Suitably, X is chlorine.

Suitably n is 1.

Suitably, compound (b) is NaClO₂.

Suitably, the water-based liquid comprises greater than 10,000 mg l⁻¹total dissolved solids (TDS). Suitably, the water-based liquid comprisesgreater than 20,000 mg l⁻¹ total dissolved solids (TDS), for examplegreater than 30,000 mg l⁻¹ TDS.

Suitably, compound (a) is TTPC.

Suitably the water-based liquid comprises a mixture of water and otherconstituents. The water-based liquid may contain oil. The water-basedliquid may comprise an oil and water emulsion. The water-based liquidmay comprise solids. The water-based liquid may comprise suspendedsolids. The water-based liquid may comprise high levels of dissolvedsolids. The water-based liquid may comprise one or more salts, forexample sodium chloride.

The water-based liquid may comprise industrial water. The water-basedliquid may consist of industrial water which may comprise water andother constituents. The water-based liquid may comprise cooling water.The water-based liquid may consist of cooling water which may comprisewater and other constituents. The water-based liquid may comprisepulping and papermaking water. The water-based liquid may consist ofpulping and papermaking water which may comprise water and otherconstituents. The water-based liquid may comprise oil and gas fieldwater. The water-based liquid may consist of oil and gas field waterwhich may comprise water and other constituents. The water-based liquidmay comprise a well treatment fluid. The water-based liquid may consistof well treatment fluid which may comprise water and other constituents.

Suitably, the method comprises treating industrial water to inhibitgrowth of one or more micro-organisms therein and/or to reduce thenumber of live micro-organisms therein. The method may comprise treatingcooling water to inhibit growth of one or more micro-organisms thereinand/or to reduce the number of live micro-organisms therein. The methodmay comprise treating pulping and papermaking water to inhibit growth ofone or more micro-organisms therein and/or to reduce the number of livemicro-organisms therein. The method may comprise treating oil and gasfield water to inhibit growth of one or more micro-organisms thereinand/or to reduce the number of live micro-organisms therein. The methodmay comprise treating a well treatment fluid to inhibit growth of one ormore micro-organisms therein and/or to reduce the number of livemicro-organisms therein.

Suitably, the method comprises adding TTPC and NaClO₂ to a water-basedliquid such that TTPC is added in an amount of 20 ppm or less and suchthat TTPC and NaClO₂ are added in a weight ratio of TTPC:NaClO₂ of from10:1 to 1:60, for example from 2:1 to 1:10.

Suitably, the method comprises treating an oil and gas field watersystem having a total dissolved solids (TDS) of 30,000 mg l−1 or greaterand wherein the method comprises adding TTPC and NaClO₂ such that TTPCis added in an amount of 20 ppm or less and such that TTPC and NaClO₂are added in a weight ratio of TTPC:NaClO₂ of from 2:1 to 1:10.

The method of the fourth aspect may comprise any feature as described inrelation to one or more of the first and/or second and/or third aspectsexcept where such features are mutually exclusive.

According to a fifth aspect of the present invention there is provided awater-based liquid incorporating a combination of:

(a) a phosphonium compound; and

(b) a compound having formula:M(XO₂)_(n)

-   -   wherein:    -   M is a Group I or Group II metal;    -   X is a halogen; and    -   n is 1 or 2.

Suitably, M is a Group I metal. Suitably M is sodium.

Suitably, X is bromine or chlorine. Suitably, X is chlorine.

Suitably n is 1.

Suitably, compound (b) is NaClO₂.

Suitably, the water-based liquid comprises greater than 10,000 mg l⁻¹total dissolved solids (TDS). Suitably, the water-based liquid comprisesgreater than 20,000 mg l⁻¹ total dissolved solids (TDS), for examplegreater than 30,000 mg l⁻¹ TDS.

Suitably, compound (a) is TTPC.

Suitably the water-based liquid comprises a mixture of water and otherconstituents. The water-based liquid may contain oil. The water-basedliquid may comprise an oil and water emulsion. The water-based liquidmay comprise solids. The water-based liquid may comprise suspendedsolids. The water-based liquid may comprise high levels of dissolvedsolids. The water-based liquid may comprise one or more salts, forexample sodium chloride.

The water-based liquid may comprise industrial water. The water-basedliquid may consist of industrial water, comprising compound (a),compound (b) and optionally other constituents in addition to water. Thewater-based liquid may comprise cooling water. The water-based liquidmay consist of cooling water, comprising compound (a), compound (b) andoptionally other constituents in addition to water. The water-basedliquid may comprise pulping and papermaking water. The water-basedliquid may consist of pulping and papermaking water, comprising compound(a), compound (b) and optionally other constituents in addition towater. The water-based liquid may comprise oil and gas field water. Thewater-based liquid may comprise oil and gas field water. The water-basedliquid may consist of oil and gas field water, comprising compound (a),compound (b) and optionally other constituents in addition to water. Thewater-based liquid may comprise a well treatment fluid. The water-basedliquid may consist of well treatment fluid, comprising compound (a),compound (b) and optionally other constituents in addition to water.

Suitably, the water-based liquid comprises TTPC in an amount of 20 ppmor less and comprises TTPC and NaClO₂ in a weight ratio of TTPC:NaClO₂of from 10:1 to 1:60, for example 2:1 to 1:10.

Suitably, the water-based liquid comprises an oil and gas field watersystem having a total dissolved solids (TDS) of 30,000 mg l⁻¹ or greaterand comprises TTPC and NaClO₂ such that TTPC is present in an amount of20 ppm or less and such that TTPC and NaClO₂ are present in a weightratio of TTPC:NaClO₂ of from 2:1 to 1:10.

The water-based liquid of the fifth aspect may comprise any feature asdescribed in relation to one or more of the first and/or second and/orthird and/or fourth aspects except where such features are mutuallyexclusive.

According to a sixth aspect of the present invention there is provided abiocidal composition comprising a combination of:

(a) a phosphonium compound; and

(b) a compound having formula:M(XO₂)_(n)

-   -   wherein:    -   M is a Group I or Group II metal;    -   X is a halogen; and    -   n is 1 or 2.

Suitably, M is a Group I metal. Suitably M is sodium.

Suitably, X is bromine or chlorine. Suitably, X is chlorine.

Suitably n is 1.

Suitably, compound (b) is NaClO₂.

Suitably, compound (a) is TTPC.

Suitably, the biocidal composition comprises one or more compounds oftype (a), one or more compounds of type (b) and water in a combinedamount of at least 50% by weight of the biocidal composition. Suitably,the biocidal composition comprises compounds (a) and (b) and water in acombined amount of at least 90% by weight of the biocidal composition.Suitably, the biocidal composition comprises compounds (a) and (b) andwater in a combined amount of at least 95% by weight of the biocidalcomposition, for example at least 99% by weight. Suitably, the biocidalcomposition consists of compounds (a) and (b) and water.

Suitably, the biocidal composition comprises compounds (a) and (b) in aweight ratio of (a):(b) of from 10:1 to 1:60, for example from 2:1 to1:10.

The biocidal composition of the sixth aspect may comprise any feature asdescribed in relation to one or more of the first and/or second and/orthird and/or fourth and/or fifth aspects except where such features aremutually exclusive.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be illustrated by way of example withreference to the following preferred embodiments.

EXAMPLES

Aqueous systems inoculated with anaerobe and facultative anaerobeculture and having a total dissolved solids (TDS) concentration of30,000 mg l⁻¹ were prepared and treated with treatment agentscomprising: (a) tri n-butyl n-tetradecyl phosphonium chloride (TTPC) and(b) NaClO₂.

TTPC was used in the form of Bellacide 350, an aqueous composition ofTTPC and water consisting of water and 50% by weight of TTPC availablefrom BWA Water Additives.

NaClO₂ was used in the form of Reagan Grade Sodium Chlorite, an 80%aqueous solution of NaClO₂ available from Amresco.

A suspension of Desulfovibrio vulgaris plus Enterobacter aerogenesbacteria containing from 1×10⁵ to 1×10⁶ cells/mL was prepared in sterilepH 8 phosphate buffer containing sodium chloride to give the desiredtotal dissolved solids (TDS) concentration. Aliquots of this suspensionwere dosed with the indicated concentrations of the compounds (a) and(b) with the concentrations being measured as ppm active. The mixtureswere allowed to stand at room temperature. At the designated contacttimes, each mixture was sampled to determine the total number of viablecells of both Desulfovibrio vulgaris and Enterobacter aerogenes byserial 10-fold dilution into API RP 38 media vials and anaerobic acidproducing media vials, respectively. The vials were incubated at 37° C.for 72 hours. Results were recorded as log₁₀ reduction in the viablecount versus the control.

The efficacy of the treatment agents was evaluated by measuring theLog₁₀ Reduction of the anaerobic bacterium Desulfovibrio vulgaris andthe facultative anaerobic bacterium Enterobacter aerogenes after contacttimes of 1 hour, 4 hours and 24 hours as detailed in Table 1. For TTPCthe stated ppm value relates to the amount of TTPC added (active). ForNaClO₂ the stated ppm relates to the amount of NaClO₂ added (active).

TABLE 1 Log₁₀ Contact Treatment agent Log₁₀ Reduction TDS time (ppmactive) Reduction Facultative Example pH (mg l⁻¹) (hours) TTPC NaClO₂Anaerobes* Anaerobes**  1(comparative) 8.0 30,000 1 6.25 — 2 0 2(comparative) 8.0 30,000 1 12.5 — 5 3  3(comparative) 8.0 30,000 1 —10 0 0  4(comparative) 8.0 30,000 1 — 20 0 0  5 8.0 30,000 1 6.25 10 5 1 6 8.0 30,000 1 6.25 20 5 1  7 8.0 30,000 1 12.5 10 5 4  8 8.0 30,000 112.5 20 5 6  9(comparative) 8.0 30,000 4 6.25 — 5 3 10(comparative) 8.030,000 4 12.5 — 5 4 11(comparative) 8.0 30,000 4 — 10 0 012(comparative) 8.0 30,000 4 — 20 1 0 13 8.0 30,000 4 6.25 10 5 6 14 8.030,000 4 6.25 20 5 6 15 8.0 30,000 4 12.5 10 5 6 16 8.0 30,000 4 12.5 205 6 17(comparative) 8.0 30,000 24 6.25 — 5 5 18(comparative) 8.0 30,00024 12.5 — 5 6 19(comparative) 8.0 30,000 24 — 10 4 0 20(comparative) 8.030,000 24 — 20 4 0 21 8.0 30,000 24 6.25 10 5 6 22 8.0 30,000 24 6.25 205 6 23 8.0 30,000 24 12.5 10 5 6 24 8.0 30,000 24 12.5 20 5 6 *5 =complete kill for anaerobes **6 = complete kill for facultativeanaerobes

The results show that surprisingly, despite NaClO₂ being ineffectivealone against anaerobes at short contact times and of limitedeffectiveness at longer contact times the combination of TTPC and NaClO₂was very effective against anaerobes, achieving complete kill (5 logreduction) at one-hour contact times.

The results with facultative anaerobes also show unexpected efficacy ofthe combination of TTPC and NaClO₂ with the combination achievingcomplete kill (6 log reduction) at 4 hours contact time.

It is particularly surprising that low levels of TTPC are effective withlow levels of NaClO₂. Accordingly, it will be appreciated that combiningTTPC and NaClO₂ may allow for less TTPC to be used to achieve kill offacultative anaerobes and anaerobes compared to TTPC alone. It will alsobe appreciated that combining TTPC and NaClO₂ may allow for completekill of facultative anaerobes and anaerobes using TTPC and NaClO₂ atcertain contact times which may not be achievable if using TTPC only.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

The invention claimed is:
 1. A method of treating an aqueous system toinhibit growth of one or more micro-organisms therein and/or to reducethe number of live micro-organisms therein, wherein the method comprisesadding treatment agents to an aqueous system having a total dissolvedsolids (TDS) of 10,000 mg l⁻¹ or greater and wherein said treatmentagents comprise: (a) tri-n-butyl n-tetradecyl phosphonium chloride(TTPC); and (b) a compound having formula:M(XO₂)_(n) wherein: M is a Group I or Group II metal; X is a halogen;and n is 1 or
 2. 2. The method according to claim 1, wherein compound(b) is NaClO₂.
 3. The method according to claim 1, wherein compound (b)is NaClO₂ and wherein the aqueous system comprises water in an amount ofup to 99% by weight.
 4. The method according to claim 1, wherein themethod comprises adding compound (a) to the aqueous system in an amountof no more than 20 ppm and/or wherein the method comprises addingcompound (b) to the aqueous system in an amount of no more than 300 ppmand/or wherein the method comprises adding compound (a) and compound (b)to the aqueous system in a combined amount of from 0.1 to 300 ppm. 5.The method according to claim 1, wherein the TDS is 30,000 mg l⁻¹ orgreater.
 6. The method according to claim 1, wherein the methodcomprises adding compound (a) and compound (b) to the aqueous system ina weight ratio of from 10:1 to 1:60.
 7. The method according to claim 1,wherein the method comprises treating the aqueous system to inhibitgrowth of anaerobic bacteria and to reduce the number of live anaerobicbacteria therein and/or wherein the method comprises treating theaqueous system to inhibit growth of aerobic bacteria and to reduce thenumber of live aerobic bacteria therein and/or wherein the methodcomprises treating the aqueous system to inhibit growth of facultativeanaerobic bacteria and to reduce the number of live facultativeanaerobic bacteria therein.
 8. The method according to claim 1, whereinthe method comprises adding TTPC and NaClO₂ to the aqueous system,wherein the TTPC is added in an amount of 20 ppm or less and the TTPCand NaClO₂ are added in a weight ratio of TTPC:NaClO₂ of from 2:1 to1:10.
 9. The method according to claim 1, wherein the aqueous system isan oil and/or gas field water system and the TDS is 30,000 mg l⁻¹ orgreater and wherein the method comprises adding TTPC and NaClO₂ to theaqueous system, wherein the TTPC is added in an amount of 20 ppm or lessand the TTPC and NaClO₂ are added in a weight ratio of TTPC:NaClO₂ offrom 2:1 to 1:10.
 10. The method according to claim 1, wherein theaqueous system comprises oil in an amount of at least 1% by weightand/or wherein the method comprises treating industrial water.
 11. Themethod according to claim 1, wherein the aqueous system is an oil and/orgas field water system and the TDS is 30,000 mg l⁻¹ or greater, whereinthe oil and gas field water system comprises oil in an amount of atleast 1% by weight, wherein compound (b) is NaClO₂, wherein the TTPC isadded in an amount of 20 ppm or less and the TTPC and NaClO₂ are addedin a weight ratio of TTPC:NaClO₂ of from 2:1 to 1:10, and wherein themethod comprises treating the aqueous system to inhibit growth ofDesulfovibrio vulgaris bacteria and Enterobacter aerogenes bacteriatherein and/or to reduce the number of live Desulfovibrio vulgarisbacteria and Enterobacter aerogenes bacteria therein.
 12. The methodaccording to claim 1, wherein the aqueous system is an oil and/or gasfield water system and the TDS is 30,000 mg l⁻¹ or greater, wherein theoil and gas field water system comprises oil in an amount of at least 1%by weight, wherein compound (b) is NaClO₂, and wherein the TTPC is addedin an amount of 20 ppm or less and the TTPC and NaClO₂ are added in aweight ratio of TTPC:NaClO₂ of from 2:1 to 1:10.
 13. The methodaccording to claim 1, wherein the method comprises treating the aqueoussystem to inhibit growth of Desulfovibrio vulgaris bacteria andEnterobacter aerogenes bacteria therein and/or to reduce the number oflive Desulfovibrio vulgaris bacteria and Enterobacter aerogenes bacteriatherein.
 14. The method according to claim 1, wherein the TDS is greaterthan 20,000 mg l⁻¹ and the method inhibits growth of one or moremicro-organisms therein and/or reduces the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to said aqueous system and wherein said treatment agents comprisea combination of: (a) tri-n-butyl n-tetradecyl phosphonium chloride(TTPC); and (b) NaClO₂; wherein the combination of TTPC and NaClO₂ areadded to the aqueous system in amounts configured to inhibit growth ofthe one or more micro-organisms therein and/or to reduce the number oflive micro-organisms therein.
 15. An aqueous system comprising acombination of: (a) tri-n-butyl n-tetradecyl phosphonium chloride(TTPC); and (b) a compound having formula:M(XO₂)_(n) wherein: M is a Group I or Group II metal; X is a halogen;and n is 1 or 2; wherein the aqueous system has a total dissolved solids(TDS) of 10,000 mg l⁻¹ or greater.
 16. A biocidal composition comprisinga combination of: (a) tri-n-butyl n-tetradecyl phosphonium chloride(TTPC); and (b) a compound having formula:M(XO₂)_(n) wherein: M is a Group I or Group II metal; X is a halogen;and n is 1 or 2; wherein the biocidal composition treats an aqueoussystem having a total dissolved solids (TDS) of 10,000 mg l⁻¹ orgreater.
 17. A method of inhibiting or preventing the growth of one ormore micro-organisms in a water-based liquid having a total dissolvedsolids (TDS) of 10,000 mg l⁻¹ or greater, wherein the method comprisesadding treatment agents to said water-based liquid and wherein saidtreatment agents comprise: (a) a phosphonium compound; and (b) acompound having formula:M(XO₂)_(n) wherein: M is a Group I or Group II metal; X is a halogen;and n is 1 or
 2. 18. The method according to claim 17, wherein themethod comprises inhibiting or preventing the growth of Desulfovibriovulgaris bacteria and Enterobacter aerogenes bacteria in the water-basedliquid.
 19. A method according to claim 17, wherein the water-basedliquid comprises Desulfovibrio vulgaris bacteria and Enterobacteraerogenes bacteria, the TDS being 30,000 mg l⁻¹ or greater, and thetreatment agents comprising: (a) tri-n-butyl n-tetradecyl phosphoniumchloride (TTPC); and (b) NaClO₂; wherein the amounts of TTPC and NaClO₂are selected such that the treatment agents provide a complete kill ofthe Desulfovibrio vulgaris bacteria and the Enterobacter aerogenesbacteria within a contact time of four hours.